1. Field of the Invention
The present invention relates to a wheel driving system for an all-terrain vehicle provided with a differential gear mechanism formed in a reduction gear case and connecting the right and the left wheel of the vehicle to a drive shaft connected to an engine.
2. Description of the Related Art
A vehicle provided with a differential gear mechanism is provided with a differential locking device, i.e., one of differential limiting devices for limiting the differential motion of the differential. The differential locking device of a dog clutch system or a spline coupling system is capable of locking the differential. Such a differential locking device is disclosed in JP-A No. Sho 59-20730.
This known differential locking device is capable of operating only in an on-off mode either to fully lock the differential or to fully free the differential. Thus, the locking operation of the differential locking device locks the differential completely regardless of the difference between loads respectively applied to the right and the left wheel and is not capable of permitting the transmission of an optional torque. When locking the differential, the differential locking device takes time in engaging the dog clutch or the spline coupling.
Another differential limiting device produces a fixed differential limiting torque by using, for example, a coned disk spring. However, the differential limiting torque of this known differential limiting device is fixed and cannot be changed according to the traveling condition or turning condition of the vehicle while the vehicle is traveling.
Accordingly, it is an object of the present invention to provide a wheel driving system capable of varying differential limiting torque applied to a differential included in a vehicle according to the difference between loads respectively applied to the right and the left wheel of a vehicle, which varies depending on the traveling condition or turning condition of the vehicle, to improve the differential performance of the differential.
Another object of the present invention is to make it possible to arrange various mechanisms such as the differential gear mechanism, the multiple-disk differential limiting mechanism and the differential limiting mechanism operating mechanism within the reduction gear case compactly.
According to one aspect of the present invention, a wheel driving system for an all-terrain vehicle provided with a differential gear mechanism having a differential case and a driven gear fastened to the differential case, formed in a reduction gear case and connecting the right and left wheels of the vehicle to a drive shaft connected to an engine comprises a multiple-disk differential limiting mechanism capable of transmitting differential limiting torque and of varying the differential limiting torque, interposed between a first rotating member on the input side of the differential gear mechanism and a second rotating member on the side of the wheel, and a differential limiting mechanism operating mechanism for operating the differential limiting mechanism to vary the differential limiting torque. The differential limiting torque can be continuously and quickly varied while the vehicle is traveling, so that the differential performance of the differential and the operability of the vehicle are improved.
In this wheel driving system, the multiple-disk differential limiting mechanism may be of a wet type immersed in an oil. In the initial stage of a differential limiting operation, the viscosity of the oil filling up gaps between friction disks can be used to produce an initial differential limiting torque. Thus, an initial differential limiting torque can be simply determined.
The differential limiting mechanism operating mechanism of the wheel driving system may include a rotatable pressing cam ring disposed on one side of an arrangement of friction disks of the multiple-disk differential limiting mechanism and a cam mechanism capable of being made to compress the friction disks by a rotation of the pressing cam ring. Thus, the differential limiting mechanism operating mechanism can be compactly arranged in the reduction gear case.
In this wheel driving system, the differential limiting mechanism operating mechanism includes a turnable operating lever disposed near a handgrip put on a handlebar of the vehicle. The differential limiting torque of the differential limiting mechanism can be easily adjusted by operating the operating lever. The working differential limiting torque can be automatically changed to an initial differential limiting torque by releasing the operating lever.
In this wheel driving system, the driven gear (34) fastened to the differential case (46) is engaged with a drive pinion (33) and the drive pinion (33) is provided on an input shaft (22) of the differential gear mechanism (30), and wherein the multiple-disk differential limiting mechanism (31) is disposed opposite to the drive pinion (33) with respect to the driven gear (34). Thus, the components of various mechanisms such as the differential gear mechanism (30), the multiple-disk differential limiting mechanism (31) and the differential limiting mechanism operating mechanism (72, 77, . . . ) can be compactly arranged within the reduction gear case (13).